This invention relates to an optical printer head, and more particularly to an optical printer head in which a plurality of luminous elements are incorporated to form an image or the like on a record medium.
Now, a conventional optical printer head in which fluorescent luminous tubes are incorporated as light sources will be described with reference to FIG. 5. The optical printer head generally designated at reference numeral 101 in FIG. 5 is arranged in the form of a write head for a fluorescent printer in a housing (not shown). The housing is provided therein with a silver salt sheet 20 in a manner to be opposite to the optical printer head 101. The silver salt sheet 20 may be constituted by a silver salt paper or a silver salt developing paper. The silver salt sheet 20 and optical printer head 101 are moved relative to each other in a sub-scanning direction or in a lateral direction in FIG. 5.
The optical printer head 101 includes three fluorescent luminous tubes 100R, 100G and 100B, which are constructed so as to emit dot-like lights of red, green and blue luminous colors from anodes 30R, 30G and 30B thereof, respectively. The anodes 30R, 30G and 30B each are constituted of a plurality of luminous dots arranged in a row or in an offset manner at predetermined intervals in a direction normal to the sheet of FIG. 5. Thus, the luminous dots of each of the fluorescent luminous tubes 100R, 100G and 100B are arranged in a main scanning direction, whereas the three fluorescent luminous tubes 100R, 100G and 100B are arranged side by side in the sub-scanning direction of the silver salt sheet 20. The printer head 101 also includes image formation elements of equi-magnification (hereinafter referred to as xe2x80x9cequi-magnification image formation elementsxe2x80x9d) 40 respectively provided for the fluorescent luminous tubes 100R, 100G and 100B and color filters 50R, 50G and 50B provided in correspondence to the respective fluorescent luminous tubes 100R, 100G and 100B and therefore the respective luminous colors. The image formation elements 40 and color filters 50R, 50G and 50B are arranged outside the fluorescent luminous tubes 100R, 100G and 100B, respectively. Three kinds of lights emitted from the luminous dots of the fluorescent luminous tubes 100R, 100G and 100B pass through the equi-magnification image formation elements 40 and color filters 50R, 50G and 50B and then are irradiated on the silver salt sheet 20, respectively.
In the conventional optical printer head 101 thus constructed, a color image is subject to color separation, to thereby provide color data on the respective colors, resulting in the fluorescent luminous tube 100R, 100G and 100B being driven by means of the color data corresponding thereto. In synchronism with such driving of the fluorescent luminous tubes 100R, 100G and 100B, the optical printer head 101 and silver salt sheet 20 are moved relative to each other in the sub-scanning direction or in the lateral direction in FIG. 5, to thereby permit dot-like light emitted from each of the fluorescent luminous tubes 100R, 100G and 100B to be irradiated on the silver salt sheet 20, resulting in a latent image being formed thereon. Then, the latent image is developed, resulting in the original color image being reproduced on the silver salt sheet 20.
The conventional optical printer head 101, as described above, is constructed so as to be moved relative to the developing paper. Such construction causes the optical printer head to require a large space, so that it is substantially impossible to form the optical printer head into a small size.
Also, in the conventional optical printer head 101, it is required to accurately align lights of three colors respectively emitted from the fluorescent luminous tubes 100R, 100G and 100B with each other on the developing paper. However, the alignment is affected by optical distortion of the equi-magnification image formation elements 40 with an increase in resolution and an increase in length of the paper, so that it is substantially difficult to attain uniform alignment of the lights over a whole width of the paper. More specifically, the equi-magnification image formation elements 40 each are formed by accumulating a plurality of bar-like lenses. Disturbance in array of the lenses causes linearity of a luminous pattern and a whole pitch thereof to be varied, leading to a variation in properties of the equi-magnification image formation element 40 depending on the element 40.
Such a variation in properties of the equi-magnification image formation elements 40 for the respective fluorescent luminous tubes 100A, 100G and 100B, even when the luminous dots or anodes 30R, 30G and 30B of the fluorescent luminous tubes 100R, 100B and 100G are uniformly arranged in juxtaposition to each other with predetermined accuracy as shown in FIG. 6, fails to permit lights of the luminous dots which permeate through the image formation elements 40 to form an image in a desired manner on the developing paper or solver salt sheet 20. Thus, an attempt to drive the fluorescent luminous tubes at predetermined timings by means of an image signal obtained by color separation to superpose dot-like lights of the respective colors on each other on the developing paper, to thereby reproduce the original color image on the developing paper results in a failure because the dot-like lights fail to be aligned with each other on the developing paper, as shown in FIG. 6.
The present invention has been made in view of the foregoing disadvantage of the prior art.
Accordingly, it is an object of the present invention is to provide an optical printer head which is capable of permitting lights emitted from a plurality of light sources to form an image on a record medium while being arranged in fixed positional relationship on the record medium, resulting in a distinct image free of color shift and color fading being formed on the record medium.
In accordance with the present invention, an optical printer head is provided. The optical printer head includes a plurality of light sources, an optical element for discharging lights introduced thereinto from said light sources in a predetermined direction therefrom while keeping axes of the lights in proximity to each other, and an image formation element of equi-magnification (hereinafter referred to as xe2x80x9cequi-magnification image formation elementxe2x80x9d) for introducing the lights discharged from the optical element thereinto.
The light sources incorporated in the optical printer head of the present invention may include at least two selected from the group consisting of a first light source for emitting light in a predetermined direction, a second light source for emitting light in a direction opposite to the first light source and a third light source for emitting light in a direction perpendicular to the first and second light sources. The optical element may be constituted by either a dichroic optical element which reflects light at a predetermined wavelength of lights emitted from the light sources and permits lights at the other wavelengths to permeate therethrough or a total reflection mirror which reflects lights emitted from the light sources. Also, the optical printer head of the present invention may also include optical members arranged in proximity to the optical element so as to permit optical path lengths of the lights of the light sources in the optical element to be substantially equal to each other. Alternatively, the optical printer head of the present invention may further include a light absorbing member arranged in proximity to the optical element so as to absorb light other than lights introduced from the light sources into the optical element.
Further, the optical printer head of the present invention may be so constructed that at least one of the light sources may be combined with an optical filter. Alternatively, the light sources each may be a monochromatic light source constituted by a combination of an optical filter which permits light at a predetermined wavelength to permeate therethrough and a fluorescent luminous tube or may contain at least one different luminous color.